CN110527809B - Preparation method of hot-rolled high-strength strip steel capable of reducing residual stress - Google Patents

Preparation method of hot-rolled high-strength strip steel capable of reducing residual stress Download PDF

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CN110527809B
CN110527809B CN201910791084.8A CN201910791084A CN110527809B CN 110527809 B CN110527809 B CN 110527809B CN 201910791084 A CN201910791084 A CN 201910791084A CN 110527809 B CN110527809 B CN 110527809B
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strip steel
cooling
strength strip
residual stress
temperature
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丁文红
王新东
齐建军
孙力
刘天武
庞博文
潘进
臧之祺
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Wuhan University of Science and Engineering WUSE
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D11/00—Process control or regulation for heat treatments
    • C21D11/005—Process control or regulation for heat treatments for cooling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
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Abstract

The invention discloses a preparation method of hot-rolled high-strength strip steel for reducing residual stress, which is characterized in that the on-line regulation and control of the residual stress are realized by controlling the quick cooling after rolling of a hot rolling unit, a continuous cooling section of the high-strength strip steel is sequentially divided into an incremental cooling section, a constant-speed cooling section and a fine-adjustment cooling section, the incremental cooling section is cooled at an incremental cooling rate, namely the cooling rate is gradually increased along with the gradual reduction of the temperature of the high-strength strip steel, and the constant-speed cooling section is cooled at a constant cooling rate. The on-line regulation and control of the residual stress in the rapid cooling process can be realized under the condition of ensuring the toughness of the material, and the cost is low.

Description

Preparation method of hot-rolled high-strength strip steel capable of reducing residual stress
Technical Field
The invention belongs to the field of hot rolling, and particularly relates to a preparation method of hot-rolled high-strength strip steel for reducing residual stress.
Background
The strip steel is widely applied to industries such as automobiles, crane booms and the like, and in order to reduce self weight and improve structural safety, the engineering machinery industry generally selects the high-strength strip steel with the yield strength Re of more than or equal to 600MPa, and the application of the high-strength strip steel with the yield strength Re of more than or equal to 980MPa is gradually increased. In order to reduce the material cost and improve the welding performance, the low-alloy component design is adopted, and the strengthening and toughness of the material are improved by refining crystal grains and controlling precipitated phases through TMCP (thermo Mechanical Control process) and a rapid cooling process, so that the development of a new generation of high-strength strip steel becomes a main way. However, the rapid cooling process introduces high residual stress into the high-strength strip steel while improving the toughness of the material, so that the problem of the residual stress of the high-strength strip steel is increasingly prominent, and the problems of material deformation, size change, even material cracking and the like in the processes of shearing, bending and welding continuously trouble the production and application enterprises of the high-strength strip steel, and people try to reduce the shape and size change of the material in the using process by controlling the straightness in the preparation process in order to reduce the level of the residual stress of the high-strength strip steel, but the yield is very low, and the one-step forming qualification rate of part of the high-strength strip steel is lower than 60%. In order to solve the above problem of residual stress, a large amount of capital and cost are consumed in the residual stress treatment, and in the precision manufacturing field where the residual stress research is relatively advanced, the cost increase due to the residual stress distortion in europe accounts for more than 4% of the whole manufacturing cost.
Tempering is a production process generally accepted by the steel industry at present for reducing the residual stress level of high-strength steel, enterprises such as Swedish SSAB, Japanese New-day iron and Bao steel occupying domestic high-grade high-strength steel markets all adopt a tempering process to regulate and control the residual stress of the high-strength steel, tempering is to heat the hot-rolled high-strength steel plate to a certain temperature below a critical temperature Ac1 (the temperature at which austenite begins to form when the steel is heated) for heat preservation so as to reduce the residual stress level of the hot-rolled high-strength steel, and the problem of the residual stress after tempering is basically controlled. However, the tempering temperature is generally 650 ℃ to 680 ℃, but test data show that after tempering at 650 ℃ for 30min, the residual stress in the high-strength steel is only reduced by 64.3%, and the critical performance of the material is also reduced, and moreover, the high-temperature tempering inevitably increases the production cost of the high-strength steel, and the tempering cost for reducing the residual stress level of the high-strength steel reaches up to 300 yuan/ton steel according to statistics, and under the background, the development of a low-cost residual stress regulation and control technology becomes a problem which is urgently desired to be solved by many manufacturers.
Disclosure of Invention
The invention aims to provide a preparation method of hot-rolled high-strength strip steel for reducing residual stress, which can realize online regulation and control of the residual stress in the rapid cooling process under the condition of ensuring the toughness of a material and has low cost.
The technical scheme adopted by the invention is as follows:
a method for preparing hot-rolled high-strength strip steel capable of reducing residual stress includes controlling quick cooling after rolling of a hot rolling unit to realize on-line regulation and control of residual stress, sequentially dividing continuous cooling interval of high-strength strip steel into an incremental cooling section, a constant-speed cooling section and a fine-adjustment cooling section, cooling in the incremental cooling section at incremental cooling speed, namely, cooling at constant cooling speed gradually increased along with gradual reduction of temperature of high-strength strip steel.
Further, the action direction of the surface temperature stress of the strip steel before phase change is controlled, so that the positive and negative of the phase change plasticity are controlled, and further the online residual stress control is realized.
Further, the temperature range of the incremental cooling section is from the finish rolling temperature to Ar3+ delta T, the temperature range of the constant-speed cooling section is from Ar3+ delta T to the finish cooling temperature, Ar3 is the phase change temperature of the high-strength strip steel, and delta T is the adjusting temperature determined according to the configuration of unit equipment.
Further, the phase transition temperature Ar3 of the high-strength strip steel is determined by firstly measuring the continuous cooling transformation CCT curve of the super-cooled austenite and then determining the phase transition temperature Ar3 of the high-strength strip steel.
Further, in the incremental cooling section, the maximum cooling rate VCoolingThe following calculation formula is satisfied,
Figure BDA0002179563310000021
in the formula, VCoolingThe maximum cooling rate; a is an adjustment coefficient; k is the heat conductivity coefficient of the high-strength strip steel; sigmasThe yield strength of the high-strength strip steel at the temperature T; alpha is the thermal expansion coefficient of the high-strength strip steel; rho is the density of the high-strength strip steel; c is the specific heat of the high-strength strip steel; e is the elastic modulus of the high-strength strip steel at the temperature T.
The invention has the beneficial effects that:
in the hot rolling process, the rapid cooling after rolling is a key step for improving the strength and toughness of the material and is also a main reason for introducing the residual stress, the method utilizes the formation mechanism of the residual stress in the cooling process and the correlation between the phase change plasticity and the temperature stress, controls the direction of the phase change plasticity strain by adjusting the action direction of the temperature stress before phase change, can realize the online regulation and control of the residual stress in the rapid cooling process under the condition of ensuring the strength and toughness of the material, can omit the tempering treatment after rolling after realizing the online regulation and control of the residual stress, and reduces the cost of steel per ton by 300 yuan/ton.
Drawings
FIG. 1 is a schematic diagram of the division of the continuous cooling zone in the embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the figures and examples.
A method for preparing hot-rolled high-strength strip steel capable of reducing residual stress comprises the steps of controlling quick cooling after rolling of a hot rolling unit to achieve on-line regulation and control of the residual stress, sequentially dividing a continuous cooling section of the high-strength strip steel into an incremental cooling section, a constant-speed cooling section and a fine-adjustment cooling section as shown in figure 1, cooling at the incremental cooling section at an incremental cooling rate, namely, the cooling rate is gradually increased along with gradual reduction of the temperature of the high-strength strip steel, and cooling at the constant-speed cooling section at a constant cooling rate. The fine cooling section is of conventional design, identical to the existing unit configuration and therefore not described. In the hot rolling process, the rapid cooling after rolling is a key step for improving the strength and toughness of the material and is also a main reason for introducing the residual stress, the method utilizes the formation mechanism of the residual stress in the cooling process and the correlation between the phase transformation plasticity and the temperature stress, controls the direction of the phase transformation plasticity strain by adjusting the action direction of the temperature stress before phase transformation, can realize the online regulation and control of the residual stress in the rapid cooling process (the regulation and control effect is different according to the type of steel and cannot be summarized), can omit the tempering treatment after rolling after the online regulation and control of the residual stress, and reduces the cost of steel per ton by 300 and 500 yuan/ton.
In the embodiment, the action direction of the surface temperature stress of the strip steel before phase transformation is controlled to control the positive and negative of the phase transformation plasticity, so that the online residual stress control is realized.
In this embodiment, the temperature range of the incremental cooling section is from the finish rolling temperature to Ar3+ Δ T, the temperature range of the constant-speed cooling section is from Ar3+ Δ T to the finish cooling temperature, Ar3 is the phase transition temperature of the high-strength strip steel (the continuous cooling transition CCT curve of the supercooled austenite is measured first, and then the phase transition temperature Ar3 of the high-strength strip steel is determined), and Δ T is the adjustment temperature determined according to the configuration of the plant equipment.
In this embodiment, the maximum cooling rate V is in the incremental cooling sectionCoolingThe following calculation formula is satisfied,
Figure BDA0002179563310000031
in the formula, VCoolingMaximum cooling rate (unit, K/s); a is an adjustment coefficient; k is the thermal conductivity (unit, W/(mK)) of the high-strength strip steel; sigmasThe yield strength (unit, MPa) of the high-strength strip steel at the temperature T; alpha is the thermal expansion coefficient (unit, 1/K) of the high-strength strip steel; rho is the density (unit, kg/m) of the high-strength strip steel3) (ii) a c is the specific heat (unit, J/(kgK)) of the high-strength strip steel; e is the modulus of elasticity (in MPa) of the high-strength steel strip at the temperature T.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.

Claims (4)

1. A preparation method of hot-rolled high-strength strip steel for reducing residual stress is characterized by comprising the following steps: the method comprises the steps of realizing on-line regulation and control of residual stress by controlling rapid cooling after rolling of a hot rolling unit, sequentially dividing a continuous cooling section of the high-strength strip steel into an incremental cooling section, a constant-speed cooling section and a fine-adjustment cooling section, cooling at the incremental cooling section at an incremental cooling rate, namely, the cooling rate is gradually increased along with the gradual reduction of the temperature of the high-strength strip steel, and cooling at the constant-speed cooling section at a constant cooling rate;
in the incremental cooling section, the maximum cooling rate
Figure DEST_PATH_IMAGE002
The following calculation formula is satisfied,
Figure DEST_PATH_IMAGE004
in the formula (I), the compound is shown in the specification,
Figure 308788DEST_PATH_IMAGE002
the maximum cooling rate;
Figure DEST_PATH_IMAGE006
to adjust the coefficient;
Figure DEST_PATH_IMAGE008
the heat conductivity coefficient of the high-strength strip steel;
Figure DEST_PATH_IMAGE010
the yield strength of the high-strength strip steel at the temperature T;
Figure DEST_PATH_IMAGE012
the thermal expansion coefficient of the high-strength strip steel is adopted;
Figure DEST_PATH_IMAGE014
the density of the high-strength strip steel;
Figure DEST_PATH_IMAGE016
the specific heat of the high-strength strip steel;
Figure DEST_PATH_IMAGE018
is the elastic modulus of the high-strength strip steel at the temperature T.
2. The method of making a hot rolled high strength strip with reduced residual stress of claim 1 wherein: by controlling the action direction of the surface temperature stress of the strip steel before phase change, the positive and negative of the phase change plasticity are controlled, and further the online residual stress control is realized.
3. The method of making a hot rolled high strength strip with reduced residual stress of claim 1 wherein: the temperature interval of the incremental cooling section is from the finishing temperature to Ar3+
Figure DEST_PATH_IMAGE020
The temperature interval of the constant speed cooling section is Ar3+
Figure 880058DEST_PATH_IMAGE020
To the final cooling temperature, Ar3 is the phase transition temperature of the high-strength strip steel,
Figure 597478DEST_PATH_IMAGE020
is the regulated temperature determined according to the configuration of the unit equipment.
4. The method of making a hot rolled high strength strip with reduced residual stress of claim 3 wherein: the phase transition temperature Ar3 of the high-strength strip steel is determined by firstly measuring a continuous cooling transformation CCT curve of the super-cooled austenite and then determining the phase transition temperature Ar3 of the high-strength strip steel.
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